1. Field of the Invention
The present invention is a coated film suitable for printing both letters and images (setting and printing), which has excellent printability using a melt thermal transfer or dot impact printer, and which is also offset printable.
2. Description of the Related Art
A melt thermal transfer printing system utilizing a thermal transfer ink sheet and a thermal head is mechanically simple and easy to maintain, and therefore has been widely used in various kinds of printers. High quality paper has been used as an image receiving sheet. Supports for the thermal transfer image receiving sheet include, for example used pulp paper; opaque synthetic paper comprising an oriented (i.e., stretched) film of propylene-based resin containing a finely divided inorganic powder such as calcined clay or calcium carbonate; and a pigment-coated type synthetic paper made by coating a pigment coating agent containing finely divided white inorganic powder and a resin binder onto a transparent polyethylene terephthalate oriented film or a transparent polyolefin film to improve the degree of whiteness and dyeability. When the thermal transfer image receiving sheet is used as a drum or container label, or as an airline shipment tag, a pressure-sensitive adhesive is coated onto the surface of the label or tag, which is opposite to the image receiving layer (back surface) of the support. The pressure-sensitive adhesive coating is also usually covered with a release paper. The release paper is peeled off before the label is adhered to a product, or before the airline shipment tag is adhered to luggage.
Labels are typically preprinted on the surface of a plastic films or paper with a frame pattern, ruled line, trade name, address, company name, etc., and optionally with specific information such as lot number, production date, bar code, etc. More recently, personal computers have been used for entered and printing such information on labels, using, for example, a melt thermal transfer printer, a wire dot printer or an ink jet printer. Thus, plastic film and paper media should be readily printed using these types of printers. Generally, paper has good printing qualities and may be used with the various kinds of printers. However, paper cannot be used if water resistance and strength are required. For these applications, plastic film has excellent water resistance and strength, but it is sometimes difficult to print on plastic using various kinds of printers. Offset printing is an inexpensive and simple printing method which generally provides clear images having the desired gradations in image density. Therefore, it is desirable to use offset printing methods to print on plastic fills. However, the inks commonly used in offset printing dry and harden at an extremely slow speed. Furthermore, since plastic films typically do not have a structure capable of absorbing ink, the ink has poor adhesion to the plastic films, and is readily peeled off. Thus, offset printing of plastic film mm is difficult.
In order to overcome these disadvantages, the present invention provides a coated film surface treated so that it can be offset printed, and also printed with thermal transfer and dot impact printers.
The present invention is a thermoplastic resin film substrate comprising an ink absorbing layer, which is suitable for melt thermal transfer printing, dot impact printing, and offset printing. The coated film of the present invention comprises a thermoplastic resin film as a support (I) having a primer coating layer (II) provided on at least one surface thereof, and further having an ink absorbing layer (III) comprising at least three kinds of inorganic pigments and a binder resin provided on the primer coating layer (III).
The ink absorbing layer (III) preferably comprises 50 to 70% by weight of inorganic pigments and 30 to 50% by weight of the binder resin. The inorganic pigment formulation may be, for example, calcium carbonate, kaolin clay and amorphous silica, preferably having weight ratios ranging from 2:1:2 to 2:3:2. It is preferable that the inorganic pigments include at least one inorganic pigment having an oil absorption of 40 to 80 ml/100 g (JIS K-5101), in an amount of 30 to 50% by weight, based on the total weight of the inorganic pigments, and include an amorphous silica having a specific surface area of 280 to 450 m2/g and a pore volume of 0.9 to 1.65 ml/g (BET method) in an amount of 15 to 20% by weight based on the total weight of the inorganic pigments.